1. Field of the Invention
The present invention relates to a novel crystalline form of a 4-[2-(2-fluorophenoxymethyl)phenyl]piperidine compound, which has activity as a serotonin (5-HT) and norepinephrine (NE) reuptake inhibitor. This invention also relates to pharmaceutical compositions comprising the crystalline compound or prepared from such compound, processes and intermediates for preparing the crystalline compound, and methods of using such compound to treat a pain disorder, such as neuropathic pain, and other ailments.
2. State of the Art
Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage (International Association for the Study of Pain (IASP), Pain Terminology). Chronic pain persists beyond acute pain or beyond the expected time for an injury to heal (American Pain Society. “Pain Control in the Primary Care Setting.” 2006:15). Neuropathic pain is pain initiated or caused by a primary lesion or dysfunction in the nervous system. Peripheral neuropathic pain occurs when the lesion or dysfunction affects the peripheral nervous system and central neuropathic pain when the lesion or dysfunction affects the central nervous system (IASP).
Several types of therapeutic agents are currently used to treat neuropathic pain including, for example, tricyclic antidepressants, serotonin and norepinephrine reuptake inhibitors, calcium channel ligands (e.g., gabapentin and pregabalin), topical lidocaine, and opioid agonists (e.g., morphine, oxycodone, methadone, levorphanol and tramadol).
4-[2-(2,4,6-Trifluorophenoxymethyl)phenyl]piperidine, described herein, inhibits the reuptake of both serotonin and norepinephrine by binding to the serotonin and norepinephrine transporters. When preparing compounds for long term storage and when preparing pharmaceutical compositions and formulations, it is often desirable to have a crystalline form of the therapeutic agent that is neither hygroscopic nor deliquescent. It is also advantageous to have a crystalline form that has a relatively high melting point (i.e. greater than about 150° C.), which allows the material to be processed, for example, micronized, without significant decomposition. Accordingly, a need exists for a stable, non-deliquescent form of 4-[2-(2,4,6-trifluorophenoxymethyl)phenyl]piperidine which has an acceptable level of hygroscopicity and a relatively high melting point.